In an open road where a vehicular road and a sidewalk are divided via sidewalk/vehicular-road boundary blocks, for example, an apron section is normally provided at a side of the vehicular road. The apron section includes a water-flow surface inclined downwardly toward a transversely outer side of the vehicular road. In such an apron section, a catch basin including a grating cover is longitudinally disposed at predetermined space intervals. The individual catch basins are interconnected by means of U-shaped ditches or water collecting pipes having a circular section, which are embedded under the apron section along the longitudinal direction.
On the water-flow surface of such an apron section at the side of the road, the occurrence of a so-called shooting flow having a small depth and high flow rate may be encountered if the inclination of the water-flow surface is increased to some degree (generally to 1% or more). Such a shooting flow passes over slots in the grating cover of the catch basin, and that may result in the vehicular-road side of the road being flooded with water.
In order to prevent the decrease of drainage performance associated with the occurrence of the aforesaid shooting flow, it may be contemplated to construct a water collecting structure wherein a guide member including a water channeling surface inclined at a greater angle than that of a water-flow slope of the water-flow surface is provided at an inlet portion (an upstream side) of the grating, whereby the shooting flow running along the guide member is positively guided into a catch passage.